The present invention relates generally to the field of electrosurgery, and more particularly to surgical devices and methods which employ high frequency electrical energy to treat tissue in regions of the head and neck, such as the ear, nose and throat. The present invention is particularly suited for treating obstructive sleep disorders, such as sleep-apnea, snoring and the like.
Sleep-apnea syndrome is a medical condition characterized by daytime hypersomnolence, intellectual deterioration, cardiac arrhythmias, snoring and thrashing during sleep. This syndrome is typically divided into two types. One type, termed “central sleep apnea syndrome”, is characterized by repeated loss of respiratory effort. The second type, termed obstructive sleep apnea syndrome, is characterized by repeated apneic episodes during sleep resulting from obstruction of the patient's upper airway.
Treatment for sleep apnea has included various medical, surgical and physical measures. Medical measures include the use of medications and the avoidance of central nervous system depressants, such as sedatives or alcohol. These measures are sometimes helpful, but rarely completely effective. Physical measures geared toward improvement have included weight loss, opening nasopharygeal airways, nasal CPAP and various dental appliances used nocturnally. These measures are cumbersome, uncomfortable and difficult to use for prolonged periods of time. In particular, CPAP devices, which act essentially as a pneumatic “splint” to the airway to alleviate the obstruction, must be used for the entire patient's lifetime, and typically requires close to 100% usage of the device while sleeping and napping. These factors result in limited patient compliance with CPAP devices, reducing the effectiveness of the therapy.
Surgical interventions have included uvulopalatopharyngoplasty (UPPP), laser-assisted uvuloplasty procedures (LAUP), tonsillectomy, surgery to correct severe retrognathia and tracheostomy. The LAUP procedures involve the use a CO2 laser to excise and vaporize excess tissue in the region of the palate and uvula. In UPPP procedures, a scalpel or conventional electrocautery device is typically employed to remove portions of the uvula, palate, pharynx and/or tonsils. While these procedures are effective, the risk of surgery in some patients is often prohibitive. In addition, UPPP and LAUP procedures performed with conventional electrocautery or laser devices typically generate extreme post-operative pain which may be unacceptable to the patient.
Recently, RF energy has been used to selectively destroy portions of the tongue and soft palate to treat air passage disorders, such as sleep apnea. This procedure, which was developed by Somnus Medical Technologies of Sunnyvale, Calif., involves the use of a monopolar electrode that directs RF current into the target tissue to desiccate or destroy submucosal tissue in the patient's mouth. Of course, such monopolar devices suffer from the disadvantage that the electric current will flow through undefined paths in the patient's body, thereby increasing the risk of unwanted electrical stimulation to portions of the patient's body. In addition, since the defined path through the patient's body has a relatively high impedance (because of the large distance or resistivity of the patient's body), large voltage differences must typically be applied between the return and active electrodes in order to generate a current suitable for ablation of the target tissue. This current, however, may inadvertently flow along body paths having less impedance than the defined electrical path, which will substantially increase the current flowing through these paths, possibly causing damage to or destroying surrounding tissue or neighboring peripheral nerves.
Another disadvantage of conventional RF devices, such as the Somnus monopolar electrode, is that these devices typically operate by creating a voltage difference between the active electrode and the target tissue, causing an electrical arc to form across the physical gap between the electrode and tissue. At the point of contact of the electric arcs with tissue, rapid tissue heating occurs due to high current density between the electrode and tissue. This high current density causes cellular fluids to rapidly vaporize into steam, thereby producing a “cutting effect” along the pathway of localized tissue heating. Thus, the tissue is parted along the pathway of evaporated cellular fluid, inducing undesirable collateral tissue damage in regions surrounding the target tissue site. This collateral tissue damage often causes indiscriminate destruction of tissue, resulting in the loss of the proper function of the tissue. In addition, the device does not remove any tissue directly, but rather depends on destroying a zone of tissue and allowing the body to eventually remove the destroyed tissue.
Yet another disadvantage with the Somnus technology is that the procedure typically takes a long time, often requiring the electrical energy to be applied to the submucosal tissue for a period of longer than a minute. This can be quite uncomfortable to the patient, who is typically awake during the procedure.
With respect to known treatments involving the debulking or removal of a selected volume of tissue from the interior or submucosal tissue of the base of the tongue (“base-of-tongue reduction”), the RF electrode or electrodes are delivered into the mouth and then inserted into the interior of the tongue through a penetration in the surface of the tongue such as the dorsum surface, the inferior dorsal surface, the ventral surface, the tip of the tongue or under the tongue sublingual surface. See for example, U.S. Pat. No. 5,800,379. By means of the electrodes, RF energy is applied to one or more treatment locations within the tongue until a selected amount of energy is applied. Typically, in base-of-tongue reduction procedures, 4 to 6 lesion are created that require 4 to 6 weeks to be reabsorbed. With this technique very little volume of the base of the tongue is removed. Due to the limitations of conventional RF devices, a greater reduction in tongue volume is not possible. Because conventional RF devices cannot actually remove any tissue directly, but rather destroy a zone of tissue (wherein the body eventually reabsorbs the destroyed tissue), to attempt to further volumetrically reduce the tongue will result in excess ablation or removal of the mucosal surface of the tongue. Excess ablation of the mucosal surface may result in nerve damage, may prolong healing, may increase the susceptibility to infection and effect speech, taste and swallowing.
As such, there is a continued interest in the development of new devices and methods for use in treating sleep obstructive disorders. In particular, it is desirable to provide devices and methods which will facilitate removal of a greater volume of tissue from the base of the tongue while overcoming the known limitations and drawbacks of the prior art, and to perform the surgery in a minimally invasive way.